1. Field of the Invention
This invention relates to machines for manufacturing lead acid type electrical storage batteries and, more particularly, to molds for casting-on of the connector straps joining the lugs on the plates of the cells and the posts employed as cell interconnectors and terminals for such batteries.
2. Description of the Prior Art
Heretofore, it has been known to cast-on the plate lug connector straps for cells, the cell posts employed to interconnect cells, and the posts forming terminals for batteries by stacking the positive and negative battery plates with suitable interleaved insulating separators, and casting the post and the straps between the lugs of the positive plates and between the lugs of the negative plates of cells while the stacks are maintained with their lugs projecting downward. U.S. Pat. Nos. 3,718,174 and 3,802,488 issued respectively Feb. 27, 1973 and Apr. 9, 1974 to Donald R. Hull and Robert D. Simonton disclose cast-on apparatus including a loading station, a casting station and an unloading station arranged so that a carriage including cell stack clamps can be moved between the stations. The casting station has a mold assembly including a flow channel for molten metal supplied at an input from a suitable reservoir and returned from an exit to that reservoir. Mold cavities are arranged along the flow channel in a pattern and form to define the straps and posts. The cavities are filled by impeding the exit of molten metal from the flow channel so that its level rises and overflows weirs intermediate the channel and cavities by flooding an internal region of the upper surface of the mold which is enclosed by a dam, thus forming a pool of molten metal. After the cavities are overflow filled, the flow channel exit is opened to permit the level of molten metal to recede and the downwardly projecting plate lugs of the cell groups retained in the carriage are lowered into the molten metal in the registering strap mold cavities. The cavities are then chilled to freeze the molten metal and the frozen straps and posts are ejected from their cavities as the carriage is elevated to raise the plates with their cast-on straps and posts for traverse to the unloading station.
In operation, the mold assemblies in the casting station are subjected to rigorous thermal requirements. The flow channel must convey molten metal throughout the freezing of metal in the cavities, hence, its walls should remain at a temperature above the freezing point of the metal. The mold cavities should have a minimum thermal inertia so they can be rapidly raised above and then chilled below the melting temperature of the metal to provide short cycle times and economic production rates. The metallurgical requirements of the operation dictate warming the mold cavities before they are filled and deoxidizing the molten metal surface before insertion of the plate lugs. These requirements are met by directing a deoxidizing flame over the upper face of the mold assembly prior to and following the overflow filling of the mold cavities.
As disclosed in the aforenoted U.S. Pat. No. 4,108,417, the desired thermal patterns in the mold assembly are achieved by utilizing a massive base for the mold assembly in which the flow channel and its input and exit are formed and by forming the mold cavities with relatively thin walls and with coolant passages in close proximity to the cavities. Advantageously, the cavities are formed in elements separate from the base and with thermal insulating barriers between them and the base so that their relatively low thermal inertia permits rapid thermal cycling without altering the base temperature to the same extremes of temperature.
Mold assemblies and battery plate stack clamps for the machines under discussion are demountable to enable the machines to be utilized in the manufacture of a number of different battery forms. Typically, lead-acid batteries are manufactured with standard case sizes and with different cell and terminal arrangements. Thus, a given overall outer dimension for the cell assembly to be housed in a given casing might be made up of six cells having eleven, thirteen, or fifteen plates per cell, having various terminal arrangements wherein the terminals are on the same side or on opposite sides, and wherein the spacings of the lug straps or terminal and connecting posts from the longitudinal center line of the battery are different.
The demountable mold assemblies are expensive. When a mold assembly is employed for strap and post configuration, a manfacturer is required to maintain a large inventory of mold assemblies, much of which is idle at any given instant.
As shown in U.S. application Ser. No. 850,100, of which this is a continuation-in-part, a typical mold has a massive base including a heavy walled elongate body containing a central flow channel for the metal to be cast and having transverse cantilever beams to present a planar I-form. The mold cavities are formed in bodies which fit between the transverse cantilever beams on each side of the elongate body with their longitudinal sides of generally vertical orientation abutting the vertical longitudinal sides of the elongate body. These abutting faces are subject to compressive forces by side plates secured to the ends of the cantilever beams as by studs tapped into bores in the beam ends. The resulting long expanse of the joint between the insert and base paralleling the flow channel tends to work and distort under the conditions of thermal cycling to which the mold is subjected such that molten metal in overflowing the joint, enters between the base and insert and ultimately develops leaks in the mold. If the width of the abutting faces of the base and insert is increased to reduce the tendency to develop leaks, the thermal conductivity increases between the massive base and the large volume portions of the insert such that the mold cycle time is increased to reduce productivity of the mold.